NASA GRAIL: Flying formation - around the moon at 3,600 MPH

An artist's depiction of the NASA GRAIL twins (Ebb and Flow) in lunar orbit. 

During GRAIL's prime mission science phase, the two spacecraft will orbit the moon as high as 31 miles (51 kilometers) and as low as 10 miles (16 kilometers). 

Credit: NASA/Caltech-JPL/MIT

The act of two or more aircraft flying together in a disciplined, synchronized manner is one of the cornerstones of military aviation, as well as just about any organized air show.

But as amazing as the U.S. Navy's elite Blue Angels or the U.S. Air Force's Thunderbirds are to behold, they remain essentially landlocked, anchored if you will, to our planet and its tenuous atmosphere.

What if you could take the level of precision of these great aviators to, say, the moon?

"Our job is to ensure our two GRAIL spacecraft are flying a very, very accurate trail formation in lunar orbit," said David Lehman, GRAIL project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We need to do this so our scientists can get the data they need."

Essentially, trail formation means one aircraft (or spacecraft in this case), follows directly behind the other. Ebb and Flow, the twins of NASA's GRAIL (Gravity Recovery And Interior Laboratory) mission, are by no means the first to synch up altitude and "air" speed while zipping over the craters, mountains, hills and rills of Earth's natural satellite.

That honour goes to the crew of Apollo 10, who in May 1969 performed a dress rehearsal for the first lunar landing but as accurate as the astronauts aboard lunar module "Snoopy" and command module "Charlie Brown" were in their piloting, it is hard to imagine they could keep as exacting a position as Ebb and Flow.

"It is an apples and oranges comparison," said Lehman. "Lunar formation in Apollo was about getting a crew to the lunar surface, returning to lunar orbit and docking, so they could get back safely to Earth. For GRAIL, the formation flying is about the science, and that is why we have to make our measurements so precisely."

As the GRAIL twins fly over areas of greater and lesser gravity at 3,600 mph (5,800 kilometers per hour), surface features such as mountains and craters, and masses hidden beneath the lunar surface, can influence the distance between the two spacecraft ever so slightly.

How slight a distance change can be measured by the science instrument beaming invisible microwaves back and forth between Ebb and Flow?

How about one-tenth of one micron? Another way to put it is that the GRAIL twins can detect a change in their position down to one half of a human hair (0.000004 inches, or 0.00001 centimeters).

For those of you who are hematologists or vampires (we are not judging here), any change in separation between the two twins greater than one half of a red corpuscle will be duly noted aboard the spacecraft's memory chips for later downlinking to Earth.

Working together, Ebb and Flow will make these measurements while flying over the entirety of the lunar surface.

Grail Twin Probe to Study Earth’s Moon Gravity Field

Two spacecrafts are set to enter orbit around Earth's moon over the New Year's weekend, in the latest lunar mission to measure the uneven gravity field and determine what lies beneath the moon' core.

The near-identical Grail spacecraft, short for Gravity Recovery and Interior Laboratory, which skyrocketed from the Florida coast in September, have been independently traveling to their destination and will arrive 24 hours apart.

On New Year's Eve, one of the Grail probes will fire its engine to slow down so that it could be captured into orbit. This move will be repeated by the other the following day.

The chances of the probes overshooting are slim since their trajectories have been precise, engineers said. Getting struck by a cosmic ray may prevent the completion of the engine burn and they won't get boosted into the right orbit.

After it enters orbit, the spacecraft will spend the next two months flying in formation and chasing one another around the moon until they are about 35 miles above the surface with an average separation of 124 miles. However, data collection won't begin until March, astronomers said.

"Both spacecraft have performed essentially flawlessly since launch, but one can never take anything for granted in this business," said mission chief scientist Maria Zuber of the Massachusetts Institute of Technology.

During the probe's orbit, changes in the lunar gravity field will cause them to speed up or slow down, changing the distance between them. Radio signals transmitted by the spacecraft will measure the slight distance gaps, allowing researchers to map the underlying gravity field.

These information can help scientists deduce what's beneath the lunar surface and explain why the far side of the moon is more rugged than the side that faces Earth.

While many new information about the moon is expected from the probes, the possibility of sending astronauts back may not happen soon as the Constellation program was canceled last year by the government.

Officially known as Grail-A and Grail-B, the name of the probes were taken from a contest hosted by NASA several months ago to submit new names. The probes will be christened with the winning names after the second orbit insertion.

ESA - Hypergravity and the Large Diameter Centrifuge

Hypergravity and the Large Diameter Centrifuge

To understand and describe the influence of gravity in systems, the observation of behaviour in microgravity and at 1g (where g is the gravitational acceleration at the surface of the Earth) is not sufficient.

A broad gravity spectrum has to be explored to complete the scientific picture of how gravity has an impact on a system: samples have to be exposed to a variety of acceleration values above 1g (hypergravity).

A Large Diameter Centrifuge (LDC) has been developed recently by ESA, allowing the acquisition of measurement points in the range from 1 to 20 g.

This document summarises the main features of the Large Diameter Centrifuge (LDC).

This instrument can provide a hypergravity environment for cells, plants and small animals, as well as physical science and technological experiments.

The LDC is part of the Life and Physical Sciences Instrumentation and Life Support Laboratory (LIS) at ESTEC (the Netherlands), dedicated to serving the science and technology user communities throughout Europe.

A wide range of hypergravity experiments can be performed in the LDC facility, including biological, biochemical, microbiological, opto-physical, physical, material and fluid sciences, geology and plasma physics.

The diameter of the LDC is eight metres. It has four arms, each of which can support two gondolas with a maximum payload of 80 kg per gondola.

In practice, six gondolas are available, plus one gondola in the centre for control or reference experiments.

The rotation of the LDC then creates the hypergravity field at the experiment site inside each gondola.

The LDC is flexible in terms of experiment scenarios, duration and possible equipment to use. This means that the system is able to execute and manage experiments that last from one minute up to six months, without stopping.

More detailed information can be found in the LDC Experimenter User Manual.

This document will be provided to the selected teams with all the information needed to perform the experiments in the LDC facility. The document addresses the general features and operations and gives more technical details and technical data of the LDC in order to facilitate the preparation of the experiment.

ISS: Keeping Rocket Engine Fuel Lines Bubble Free in Space

Astronaut Scott Kelley installing the Capillary Channel Flow, or CCF, in the Microgravity Science Glovebox, or MSG, on board the International Space Station. 

Photo Credit NASA.

Without gravity in the space environment, how do you keep the fuel contained so it can be transported to where it is needed? How do you keep gas bubbles out of the fuel lines?

Being able to use all of the fuel in a spacecraft tank has been an ongoing challenge in spacecraft design for the past 50 years, but great advances on the problem are being made using the International Space Station as a laboratory. In the microgravity of space, the "bottom" of the tank is NOT apparent.

When a spacecraft tank is nearly full, the fuel tends to "cling" to all sides of the tank leaving a small gas bubble, or ullage, near the center of the tank. Once the tank has emptied to the point where there is not enough liquid to cover the walls of the tank, it is not clear where the remaining fluid is "positioned."

Here on Earth this is not an issue. For example, in the gasoline tank in your car, gravity always positions the remaining fluid at the bottom of the tank, allowing the car's fuel pump to draw the last bit of fuel from the tank.

"Presently, the low risk solution to this problem is to size the fuel tank larger than what is needed for the mission, but this adds extra launch mass and volume to the spacecraft," states Robert Green at NASA's Glenn Research Center.

Another method is to add special channel-like structures, called vanes, inside the tank to purposely "wick" the remaining fuel to the exit. A key area of study is how different shapes of channels work and whether they remove any gas bubbles that can get captured in the flow.

ESA scientists from Germany and the U.S. have been studying these processes as part of an investigation called Capillary Channel Flow, or CCF. The CCF study looks at several capillary channel geometries that mimic the shape and physical characteristics of vanes in fuel tanks.

One set of capillary channel geometries was developed by Michael E. Dreyer at the Center of Applied Space Technology and Microgravity, or ZARM, at the University of Bremen in Bremen, Germany, and sponsored by the German Aerospace Center, or DLR.

The geometries included parallel plates and square-grooves. This part of the investigation was completed in March 2011, after 78 days of nearly continuous ground-controlled operation.

The second set of channel geometries was designed by Mark M. Weislogel at Portland State University in Portland, Ore. Sponsored by NASA, it will begin operation this month. The geometry is a wedge-shaped channel with only one side exposed to the interior of the tank. Weislogel is studying the fluid behaviour in the interior corner where the two plates meet.

In the absence of gravity, surface tension

In the absence of gravity, surface tension dominates the physics of fluids. Here, in an image taken on the International Space Station, it causes water to extend from a metal loop as if it were stirred by an invisible spoon.

This stirring effect was created by using a flashlight to unevenly heat the water. The resulting temperature difference induced an imbalance in the surface tension, causing the fluid to rotate.

Such surface-tension-triggered movement, called Marangoni convection, is less obvious on Earth, but can be seen in environments such as cooling puddles of molten steel.